A reproduction of the fragmentary Fasti Antiates Maiores(c. 60BC), with the seventh and eighth months still named Quintilis ("QVI") and Sextilis ("SEX") and an intercalary month ("INTER") in the far righthand column

Roman dates were counted inclusively forward to the next of three principal days: the first of the month (the kalends), a day shortly before the middle of the month (the ides), and eight days—nine, counting inclusively—before this (the nones). The original calendar consisted of ten months beginning in spring with March; winter was left as an unassigned span of days. These months ran for 38 nundinal cycles, each forming an eight-day week (nine days counted inclusively, hence the name) ended by religious rituals and a public market. The winter period was later divided into two months, January and February. The legendaryearly kingsRomulus and Numa Pompilius were traditionally credited with establishing this early fixed calendar, which bears traces of its origin as an observational lunar one. In particular, the kalends, nones, and ides seem to have derived from the first sighting of the crescent moon, the first-quarter moon, and the full moon respectively. The system ran well short of the solar year, and it needed constant intercalation to keep religious festivals and other activities in their proper seasons. This is a typical element of lunisolar calendars. For superstitious reasons, such intercalation occurred within the month of February even after it was no longer considered the last month.

After the establishment of the Roman Republic, years began to be dated by consulships and control over intercalation was granted to the pontifices, who eventually abused their power by lengthening years controlled by their political allies and shortening the years in their rivals' terms of office. Having won his war with Pompey, Caesar used his position as Rome's chief pontiff to enact a calendar reform in 46BC, coincidentally making the year of his third consulship last for 446days. In order to avoid interfering with Rome's religious ceremonies, the reform added all its days towards the ends of months and did not adjust any nones or ides, even in months which came to have 31days. The Julian calendar was supposed to have a single leap day on 24 February (a doubled VI Kal.Mart.) every fourth year but following Caesar's assassination the priests figured this using inclusive counting and mistakenly added the bissextile day every three years. In order to bring the calendar back to its proper place, Augustus was obliged to suspend intercalation for one or two decades. The revised calendar remained slightly longer than the solar year; by the 16th century the date of Easter had shifted so far away from the vernal equinox that Pope Gregory XIII ordered the calendar’s adjustment, resulting in the Gregorian calendar.

The original Roman calendar is believed to have been an observational lunar calendar[1] whose months began from the first signs of a new crescent moon. Because a lunar cycle is about ​291⁄2 days long, such months would have varied between Template:Npwrap. Twelve such months would have fallen 10 or 11 days short of the solar year; without adjustment, such a year would have quickly rotated out of alignment with the seasons in the manner of the Islamic calendar. Given the seasonal aspects of the later calendar and its associated religious festivals, this was presumably avoided through some form of intercalation or the suspension of the calendar during winter.

The Romans themselves described their first organized year as one with ten fixed months, each of 30 or 31 days.[2][3] Such a decimal division fitted general Roman practice.[4] The four 31 day months were called "full" (pleni) and the others "hollow" (cavi).[5][6] Its 304 days made up exactly 38 nundinal cycles. The system is usually said to have left the remaining 50 odd days of the year as an unorganized "winter", although Licinius Macer's lost history apparently stated the earliest Roman calendar employed intercalation instead[7][8] and Macrobius claims the 10 month calendar was allowed to shift until the summer and winter months were completely misplaced, at which time additional days belonging to no month were simply inserted into the calendar until it seemed things were restored to their proper place.[9][10]

Later Roman writers credited this calendar to Romulus,[11][12] their legendaryfirst king and culture hero, although this was common with other practices and traditions whose origin had been lost to them. Some scholars doubt the existence of this calendar at all, as it is only attested in late Republican and Imperial sources and supported only by the misplaced names of the months from September to December.[13]Rüpke also finds the coincidence of the length of the supposed "Romulan" year with the length of the first ten months of the Julian calendar to be suspicious.[clarification needed][13]

Other traditions existed alongside this one, however. Plutarch's Parallel Lives recounts that Romulus's calendar had been solar but adhered to the general principle that the year should last for 360 days. Months were employed secondarily and haphazardly, with some counted as 20 days and others as 35 or more.[17][18]

The attested calendar of the Roman Republic was quite different. It followed Greek calendars in assuming a lunar cycle of ​291⁄2 days and a solar year of ​121⁄2synodic months (​3683⁄4 days), which align every fourth year after the addition of two intercalary months.[6] Two months were added at the end of the year to complete the cycle during winter, January and February, before the intercalary month inserted every two years; the intercalary month was sometimes known as Mercedonius.[6]

The Romans did not follow the usual Greek practice in alternating 29- and 30-day months and a 29- or 30-day intercalary month every other year. Instead, their 1st, 3rd, 5th, and 8thmonths[a] had 31days each; all the other months had 29days except February, which had 28days for three years and then 29 every fourth year. The total of these months over 4years differed from the Greeks by 5days, meaning the Roman intercalary month always had 27days. Similarly, within each month, the weeks did not vary in the Greek fashion between 7 and 8 days; instead, the full months had two additional days in their first week and the other three weeks of every month ran for 8days ("nine" by Roman reckoning).[19] Still more unusually, the intercalary month was not placed at the end of the year but within the month of February after the Terminalia on the 23rd (a.d.VIIKal.Mart.); the remaining days of February followed its completion (these last 6 or 7 days of February were actually named and counted inclusively in days before the calends of March and were traditionally part of the celebration for the new year). This seems to have arisen from Roman superstitions concerning the numbering and order of the months.[citation needed] The arrangement of the Roman calendar similarly seems to have arisen from Pythagorean superstitions concerning the luckiness of odd numbers.[19]

According to Livy's Periochae, the beginning of the consular year changed from March to January1 in 154BC to respond to a rebellion in Hispania.[24] Plutarch believed Numa was responsible for placing January and February first in the calendar;[17][18]Ovid states January began as the first month and February the last, with its present order owing to the Decemvirs.[25][26]W. Warde Fowler believed the Roman priests continued to treat January and February as the last months of the calendar throughout the Republican period.[27]

The consuls' terms of office were not always a modern calendar year, but ordinary consuls were elected or appointed annually. The traditional list of Roman consuls used by the Romans to date their years began in 509BC.[30]

Gnaeus Flavius, a secretary (scriba) to censor App. Claudius Caecus introduced a series of reforms in 304BC.[31] Their exact nature is uncertain, although he is thought to have begun the custom of publishing the calendar in advance of the month, depriving the priests of some of their power but allowing for a more consistent calendar for official business.[32]

Julius Caesar, following his victory in his civil war and in his role as pontifex maximus, ordered a reformation of the calendar in 46BC. This was undertaken by a group of scholars apparently including the AlexandrianSosigenes[33] and the Roman M. Flavius.[34][29] Its main lines involved the insertion of ten additional days throughout the calendar and regular intercalation of a single leap day every fourth year to bring the Roman calendar into close agreement with the solar year. The year 46BC was the last of the old system and included 3 intercalary months, the first inserted in February and two more—Intercalaris Prior and Posterior—before the kalends of December.

In large part, this calendar continued unchanged under the Roman Empire. (Egyptians used the related Alexandrian calendar, which Augustus had adapted from their wandering ancient calendar to maintain its alignment with Rome's.) A few emperors altered the names of the months after themselves or their family, but such changes were abandoned by their successors. Diocletian began the 15-year indiction cycles beginning from the AD297 census;[30] these became the required format for official dating under Justinian. Constantine formally established the 7-day week by making Sunday an official holiday in 321.[citation needed] Consular dating became obsolete following the abandonment of appointing nonimperial consuls in AD541.[30] The Roman method of numbering the days of the month never became widespread in the Hellenized eastern provinces and was eventually abandoned by the Byzantine Empire in its calendar.

Nones (Nonae or Non.), the 7thday of full months[38] and 5thday of hollow ones,[37] 8days—"nine" by Roman reckoning—before the Ides in every month

Ides (Idus, variously Eid. or Id.), the 15thday of full months[38] and the 13thday of hollow ones,[37] a day less than the middle of each month

These are thought to reflect a prehistoric lunar calendar, with the kalends proclaimed after the sighting of the first sliver of the new crescent moon a day or two after the new moon, the nones occurring on the day of the first-quarter moon, and the ides on the day of the full moon. The kalends of each month were sacred to Juno and the ides to Jupiter.[39][40] The day before each was known as its eve (pridie); the day after each (postridie) was considered particularly unlucky.

The days of the month were expressed in early Latin using the ablative of time, denoting points in time, in the contracted form "the 6thDecember Kalends" (VI Kalendas Decembres).[38] In classical Latin, this use continued for the three principal days of the month[41] but other days were idiomatically expressed in the accusative case, which usually expressed a duration of time, and took the form "6th day before the December Kalends" (ante diem VI Kalendas Decembres). This anomaly may have followed the treatment of days in Greek,[42] reflecting the increasing use of such date phrases as an absolute phrase able to function as the object of another preposition,[38] or simply originated in a mistaken agreement of dies with the preposition ante once it moved to the beginning of the expression.[38] In late Latin, this idiom was sometimes abandoned in favor of again using the ablative of time.

The kalends were the day for payment of debts and the account books (kalendaria) kept for them gave English its word calendar. The public Roman calendars were the fasti, which designated the religious and legal character of each month's days. The Romans marked each day of such calendars with the letters:[43]

F (fastus, "permissible") on days when it was legal to initiate action in the courts of civil law (dies fasti, "allowed days")

C (comitialis) on fasti days during which the Roman people could hold assemblies (dies comitiales)

N (nefastus) on days when political and judicial activities were prohibited (dies nefasti)

QRCF (uncertain)[f] on days when the "king" (rex sacrorum) could convene an assembly

EN (endotercissus, an archaic form of intercissus, "halved") on days when most political and religious activities were prohibited in the morning and evening due to sacrifices being prepared or offered but were acceptable for a period in the middle of the day

Each day was also marked by a letter from A to H to indicate its place within the nundinal cycle of market days.

The nundinae were the market days which formed a kind of weekend in Rome, Italy, and some other parts of Roman territory. By Roman inclusive counting, they were reckoned as "ninth days" although they actually occurred every eighth day. Because the republican and Julian years were not evenly divisible into eight-day periods, Roman calendars included a column giving every day of the year a nundinal letter from A to H marking its place in the cycle of market days. Each year, the letter used for the markets would shift 2–5 letters along the cycle. As a day when the city swelled with rural plebeians, they were overseen by the aediles and took on an important role in Roman legislation, which was supposed to be announced for three nundinal weeks (between 17 and 24 days) in advance of its coming to a vote. The patricians and their clients sometimes exploited this fact as a kind of filibuster, since the tribunes of the plebs were required to wait another three-week period if their proposals could not receive a vote before dusk on the day they were introduced. Superstitions arose concerning the bad luck that followed a nundinae on the nones of a month or, later, on the first day of January. Intercalation was supposedly used to avoid such coincidences, even after the Julian reform of the calendar.

The names of Roman months originally functioned as adjectives (e.g., the January kalends occur in the January month) before being treated as substantive nouns in their own right (e.g., the kalends of January occur in January). Some of their etymologies are well-established: January and March honor the gods Janus[46] and Mars;[47] July and August honor the dictatorJulius Caesar[48] and his successor, the emperorAugustus;[49] and the months Quintilis,[50] Sextilis,[51] September,[52] October,[53] November,[54] and December[55] are archaic adjectives formed from the ordinal numbers from 5 to 10, their position in the calendar when it began around the spring equinox in March.[52] Others are uncertain. February may derive from the Februa festival or its eponymous februa ("purifications, expiatory offerings"), whose name may be either Sabine or preserve an archaic word for sulphuric.[56] April may relate to the Etruscan goddess Apru or the verb aperire ("to open").[citation needed] May and June may honor Maia[57] and Juno[58] or derive from archaic terms for "senior" and "junior". A few emperors attempted to add themselves to the calendar after Augustus, but without enduring success.

In classical Latin, the days of each month were usually reckoned as:[41]

Dates after the ides count forward to the kalends of the next month and are expressed as such. For example, March19 was expressed as "the 14th day before the April Kalends" (a.d. XIV Kal. Apr.), without a mention of March itself. The day after a kalends, nones, or ides was also often expressed as the "day after" (postridie) owing to their special status as particularly unlucky "black days".

The anomalous status of the new 31-day months under the Julian calendar was an effect of Caesar's desire to avoid affecting the festivals tied to the nones and ides of various months. However, because the dates at the ends of the month all counted forward to the next kalends, they were all shifted by one or two days by the change. This created confusion with regard to certain anniversaries. For instance, Augustus's birthday on the 23rdday of September was a.d. VIII Kal. Oct. in the old calendar but a.d. IX Kal. Oct. under the new system. The ambiguity caused honorary festivals to be held on either or both dates.

The Republican calendar only had 355days, which meant that it would quickly unsynchronize from the solar year, causing, for example, agricultural festivals to occur out of season. The Roman solution to this problem was to periodically lengthen the calendar by adding extra dayswithin February. February was broken into two parts, each with an odd number of days. The first part ended with the Terminalia on the 23rd (a.d. VII Kal. Mart.), which was considered the end of the religious year; the five remaining days beginning with the Regifugium on the 24th (a.d. VI Kal. Mart.) formed the second part; and the intercalary month Mercedonius was inserted between them. In such years, the days between the ides and the Regifugium were counted down to either the Intercalary Kalends or to the Terminalia. The intercalary month counted down to nones and ides on its 5th and 13th day in the manner of the other short months. The remaining days of the month counted down towards the March Kalends, so that the end of Mercedonius and the second part of February were indistinguishable to the Romans, one ending on a.d. VII Kal. Mart. and the other picking up at a.d. VI Kal. Mart. and bearing the normal festivals of such dates.

Apparently because of the confusion of these changes or uncertainty as to whether an intercalary month would be ordered, dates after the February ides are attested as sometimes counting down towards the Quirinalia (Feb.17), the Feralia (Feb.21), or Terminalia (Feb.23)[59] rather than the intercalary or March kalends.

The third-century writer Censorinus says:

When it was thought necessary to add (every two years) an intercalary month of 22 or 23 days, so that the civil year should correspond to the natural (solar) year, this intercalation was in preference made in February, between Terminalia [23rd] and Regifugium [24th].[60]

The fifth-century writer Macrobius says that the Romans intercalated 22 and 23 days in alternate years (Saturnalia, 1.13.12); the intercalation was placed after 23February and the remaining five days of February followed (Saturnalia, 1.13.15). To avoid the nones falling on a nundine, where necessary an intercalary day was inserted "in the middle of the Terminalia, where they placed the intercalary month".[61]

This is historically correct. In 167BC Intercalaris began on the day after 23February [62] and in 170BC it began on the second day after 23February.[63]Varro, writing in the first centuryBC, says "the twelfth month was February, and when intercalations take place the five last days of this month are removed."[64] Since all the days after the Ides of Intercalaris were counted down to the beginning of March Intercalaris had either 27days (making 377 for the year) or 28 (making 378 for the year).

There is another theory which says that in intercalary years February had 23 or 24 days and Intercalaris had 27. No date is offered for the Regifugium in 378-day years.[65] Macrobius describes a further refinement whereby, in one 8-year period within a 24-year cycle, there were only three intercalary years, each of 377days. This refinement brings the calendar back in line with the seasons, and averages the length of the year to 365.25days over 24years.

The Pontifex Maximus determined when an intercalary month was to be inserted. On average, this happened in alternate years. The system of aligning the year through intercalary months broke down at least twice: the first time was during and after the Second Punic War. It led to the reform of the 191 BCAcilian Law on Intercalation, the details of which are unclear, but it appears to have successfully regulated intercalation for over a century. The second breakdown was in the middle of the first century BC and may have been related to the increasingly chaotic and adversarial nature of Roman politics at the time. The position of Pontifex Maximus was not a full-time job; it was held by a member of the Roman elite, who would almost invariably be involved in the machinations of Roman politics. Because the term of office of elected Roman magistrates was defined in terms of a Roman calendar year, a Pontifex Maximus would have reason to lengthen a year in which he or his allies were in power or shorten a year in which his political opponents held office.

Although there are many stories to interpret the intercalation, a period of 22 or 23 days is always ​1⁄4synodic month short. Obviously, the month beginning shifts forward (from the new moon, to the third quarter, to the full moon, to the first quarter, back the new moon) after intercalation.

As mentioned above, Rome's legendary 10-month calendar notionally lasted for 304days but was usually thought to make up the rest of the solar year during an unorganized winter period. The unattested but almost certain lunar year and the pre-Julian civil year were 354 or 355 days long, with the difference from the solar year more or less corrected by an irregular intercalary month. The Julian year was 365days long, with a leap day doubled in length every fourth year, almost equivalent to the present Gregorian system.

The Romans did not have records of their early calendars but, like modern historians, assumed the year originally began in March on the basis of the names of the months following June. The consul M. Fulvius Nobilior (r.189BC) wrote a commentary on the calendar at the Temple of Hercules Musarum that claimed January had been named for Janus because the god faced both ways,[68][where?] suggesting it had been instituted as a first month.[citation needed] It was, however, usually said to have been instituted along with February, whose nature and festivals suggest it had originally been considered the last month of the year. The consuls' term of office—and thus the order of the years under the republic—seems to have changed several times. Their inaugurations were finally moved to 1January (Kal. Ian.) in 153BC to allow Q. Fulvius Nobilior to attack Segeda in Spain during the Celtiberian Wars, before which they had occurred on 15March (Eid. Mart.).[69] There is reason to believe the inauguration date had been 1May during the 3rd century BC until 222BC[citation needed] and Livy mentions earlier inaugurations on 15May (Eid. Mai.), 1July (Kal. Qui.), 1August (Kal. Sex.), 1October (Kal. Oct.), and 15December (Eid. Dec.).[70][where?] Under the Julian calendar, the year began on 1January but years of the Indiction cycle began on 1September.

The continuity of names from the Roman to the Gregorian calendar can lead to the mistaken belief that Roman dates correspond to Julian or Gregorian ones. In fact, the essentially complete list of Roman consuls allows general certainty of years back to the establishment of the republic but the uncertainty as to the end of lunar dating and the irregularity of Roman intercalation means that dates which can be independently verified are invariably weeks to months outside of their "proper" place. Two astronomical events dated by Livy show the calendar 4 months out of alignment with the Julian date in 190BC and 2 months out of alignment in 168BC. Thus, "the year of the consulship of Publius Cornelius Sciopio Africanus and Publius Licinius Crassus" (usually given as "205BC") actually began on 15March 205BC and ended on 14March 204BC according to the Roman calendar but may have begun as early as November or December 206BC owing to its misalignment. Even following the establishment of the Julian calendar, the leap years were not applied correctly by the Roman priests, meaning dates are a few days out of their "proper" place until a few decades into Augustus's reign.

Given the paucity of records regarding the state of the calendar and its intercalation, historians have reconstructed the correspondence of Roman dates to their Julian and Gregorian equivalents from disparate sources. There are detailed accounts of the decades leading up to the Julian reform, particularly the speeches and letters of Cicero, which permit an established chronology back to about 58BC. The nundinal cycle and a few known synchronisms—e.g., a Roman date in terms of the Attic calendar and Olympiad—are used to generate contested chronologies back to the start of the First Punic War in 264BC. Beyond that, dates are roughly known based on clues such as the dates of harvests and seasonal religious festivals.

^That is, the 3rd, 5rd, 7th, and 10th months after the repositioning of January and February.

^Plutarch reports this tradition while claiming that the months had more probably predated or originated with Romulus.[17][18]

^This equivalence was first described by Stanyan in his history of ancient Greece.[23]

^There are some documents which state the month had been renamed as early as 26 or 23BC, but the date of the Lex Pacuvia is certain.

^The NP days are sometimes thought to mark days when political and judicial activities were prohibited only until noon, standing for nefastus priore.

^The QRCF days are sometimes supposed, on the basis of the Fasti Viae Lanza which gives it as Q. Rex C. F., to stand for "Permissible when the King Has Entered the Comitium" (Quando Rex Comitiavit Fas).[44]

^The original 31-day months of the Roman calendar were March, May, Quintilis or July, and October.

^The 31-day months established by the Julian reform were January, Sextilis or August, and December. The other 31-day months of the Julian calendar continued to use the old system, with their Nones on the 7th and Ides on the 15th.

^The 30-day months established by the Julian reform were April, June, September, and November.

^The 29-day months of the calendar prior to the Julian reform were January, April, June, Sextilis, September, November, and December. After the Julian reform, February could have 29 days during a leap year but it was not reckoned according to this list until late in the imperial period. Instead, the sixth day before the March Kalends was initially treated as lasting for 48 hours.

^After the Julian reform, this day was reckoned to last 48 hours during a leap year.

^47.13 and 47.14: "[47.13] In the five hundred and ninety-eighth year after the founding of the city, the consuls began to enter upon their office on 1January. [47.14] The cause of this change in the date of the elections was a rebellion in Hispania."